Toward a new method to estimate underwater light regime under spatially heterogeneous surface environments in the Arctic

Philippe Massicotte

Guislain Bécu

Simon Lambert-Girard

Julien Laliberté

Marcel Babin

Toward a new method to estimate underwater light regime under spatially heterogeneous surface environments in the Arctic

Philippe Massicotte, Guislain Bécu, Simon Lambert-Girard, Julien Laliberté, Marcel Babin

Under water light field

The characteristics of under water light field are very important drivers of ecosystem functioning:

  • Primary production

  • Photo-chemical reactions (photo-degradation)

  • Energy budget in the water column

Measuring light in open water

Nowadays, measuring downwelling irradiance (\(E_d\)) in open water is pretty straightforward.

Caption for the picture.

Typical under water light profiles

In open water, downwelling irradiance (\(E_d\)) is known to decrease exponentially with increasing depth.

Mathematical formulation

\[ \text{Ed}(z) = Ed(0) \times e^{-k \times d} \]

  • \(k\) is the vertical diffuse attenuation coefficients describing the rate at which light decreases with increasing depth.

  • Important metric used by biologists and to parameterize models (need for precise estimates).

An example

Problematics

Due to spatial horizontal heterogeneity, measuring vertical light profiles under ice cover present considerable challenges in comparison to open water.

PHOTO MELT PONDS

What is seen by the radiometer

Light measured under ice

As a consequence, light transmission can increase to reach a subsurface maximum between 5 and 10 meters.

Estimating K underice

Obviously, estimating \(K_{ed}\) under ice represent a considerable challenge.

Estimating K underice

Influence of the horizontal heterogeneity on measured light.

what image shows

Estimating K underice

Due to the horizontal heterogeneity, measured light properties are only valid locally and cannot be generalized to the surrounding environment.

Objectives

  1. New method to have adequate light estimates under horizontally heterogeneous ice sheet

Lu

Caption for the picture.

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Acknowledgements

The GreenEdge project is funded by the following French and Canadian programs and agencies: ANR (Contract #111112), CNES (project #131425), IPEV (project #1164), CSA, Fondation Total, ArcticNet, LEFE and the French Arctic Initiative (GreenEdge project). This project would not have been possible without the support of the Hamlet of Qikiqtarjuaq and the members of the community as well as the Inuksuit School and its Principal Jacqueline Arsenault. The project is conducted under the scientific coordination of the Canada Excellence Research Chair on Remote sensing of Canada’s new Arctic frontier and the CNRS & Université Laval Takuvik Joint International laboratory (UMI3376). The field campaign was successful thanks to the contribution of J. Ferland, G. Bécu, C. Marec, J. Lagunas, F. Bruyant, J. Larivière, E. Rehm, S. Lambert-Girard, C. Aubry, C. Lalande, A. LeBaron, C. Marty, J. Sansoulet, D. Christiansen-Stowe, A. Wells, M. Benoît-Gagné, E. Devred and M.-H. Forget from the Takuvik laboratory, C.J. Mundy and V. Galindo from University of Manitoba as well as F. Pinczon du Sel and E. Brossier from Vagabond. We also thank Michel Gosselin, Québec-Océan, the CCGS Amundsen and the Polar Continental Shelf Program for their in-kind contribution in polar logistic and scientific equipment.